>>I'm not sure exactly what you want.  I feel like I should, but I haven't
>>had breakfast yet!

>>But I can see the core of what you want: event A happens, then at some
>>time T later you want code B to execute.  Usually the way that I do this
>>in a non-interrupt-driven system is to set up one of the processor clocks
>>to free run, then on the event set

>>extern int time_now; // set by hardware
>>int timeout;

>>timeout = time_now + T;
>>enabled = true;

>>Then in my task loop I'll have a check

>>if (enabled == true && time_now - timeout > 0)
>>{
>> // put your code here
>>}

>>Note that the order of operations in the test is important: time_now
>>_will_ roll over; if you test on time_now > timeout you will get
>>different, and quite possibly undesired, behavior from your code.  Note
>>also that whatever size your 'int' is (probably 16 bits), this method
>>will only support a timeout of MAX_INT (32767, if 16 bits) ticks.

>>Alternately, you can have a routine that just runs at 1ms intervals, and
>>keep track of all your timers there.

>>--
>>Tim Wescott
>>Control system and signal processing consulting
>>www.wescottdesign.com

> Oops, something I didn't make clear.. millis() is part of the Arduino
> functions.
> From Arduio Reference:

> millis()
> Description
> Returns the number of milliseconds since the Arduino board began running the
> current program. This number will overflow (go back to zero), after
> approximately 50 days.

> So what I want to do is make my loop run as fast as it can and control by
> setting flags and conditions, sort of parallel processing like in a PLC, not
> sequential style programming.

> A little background.  My first computer was a sinclare zx 80 (IIRC) for
> $199, later I bought a Commodore 64, did some Basic and 6502 assembly
> language.  Later I played with PIC microcontrollers, 16C84, 16f84 came out
> later.  So about everything I learned was pretty much sequential style
> programming.  When I got a 286/12 I bought Turbo C++ and a "Teach yourself
> C" book, got where I could write programs but not enough practice to get
> good at it.  After some time I ended up with an Engineering company that did
> industrial automation type work.  It was difficult at first for me to get
> PLC's to work like I wanted, I was used to writing sequential type of
> programs and the PLC was parallel, all rungs execute at the same time, well,
> not really but I learned that I should write programs as if they did.

> Here's a project I designed, built, and programmed the controls for.

> http://www.youtube.com/watch?v=9xFwpbpusTo

> You can see there are a lot of things happening at once.

> Anyway, over the years I have pretty much figured out how I can write the
> same type of programming in other languages beside ladder logic.  The
> straight runs just AND and OR conditions to control outputs when they should
> be according to the logic.  I think I could write the bulb machine program
> in 'C' very much like it was written in ladder logic.

> One of the problem areas is getting timers to work like PLC timers, they can
> have dozens timing multiple events at once, none interfering with the
> others.  So I'm trying to come up with a good function that will compare the
> preset time with the system time and execute additional code 1 pass per pass
> through the loop (won't hang up the loop).

> Now I know I can write something to hog the processor with a loop and halt
> the main loop, but I will have to be careful not to, if it happens I will
> have to correct the error.

> The system timer will overflow once every 50 days so I need to set an
> "will_overflow_bit" when the destination time is less than the current time
> ( a positive number plus a positive number is greater unless there is an
> overflow).  So once the timer condition is true, and the timer preset is
> timed out, the code will be executed once per loop, like an if() function,
> not cycled inside continuously like a while() function.

> RogerN